noun: the force attracting atoms to each other and binding them together in a molecule (Example: "Basic dyes have an affinity for wool? and silk?")

noun: (immunology) the attraction between an antigen? and an antibody?

noun: a close connection marked by community of interests or similarity in nature or character (Example: "Found a natural affinity with the immigrants")

noun: (biology) state of relationship between organisms or groups of organisms resulting in resemblance in structure or structural parts (Example: "In anatomical structure prehistoric man shows close affinity with modern humans")